This invention relates to the deposition of a coating on a substrate by such vacuum techniques as sputtering, thermal evaporation, and arc evaporation and, in particular to the deposition of such coatings comprising two or more components in which the relative percentages of the components change through the coating thickness.
In a publication by Thornton and Lamb, Thin Solid Films, 96(1982) pp. 175-183, there is disclosed a multi-source deposition configuration utilized in a vacuum chamber, see FIG. 7 of the present application. In particular, two or more cathodes are mounted facing a rotating substrate (or array of substrates), with the power to one or more of the cathodes being changed as a function of time during the deposition process, so as to change the deposition rate of one material, and therefore change the composition of the coating as its thickness increases. The power may be increased or decreased so as to produce an arbitrary composition profile. This is effected with the only motion of the substrate being rotation, there being no provision to translate the substrates through the chamber during the deposition process. The shields indicated serve to improve the deposition rate uniformity along the length of the cathode and do not influence the grading of the coating composition.
In a further publication by Thornton and Lamb, Final Report to Solar Energy Research Institute, Contract No. XP-9-8260-1, December 1982, a similar technique to that of FIG. 7 is described in which multiple substrates are coated in a single batch as illustrated in FIG. 8. In particular, Pt/Al.sub.2 0.sub.3 graded cermet coatings are deposited on tubular substrates.
As will be described hereinafter, masking techniques are advantageously employed in the present invention utilizing one or more shaped aperture shields. Such shields have also been used in the prior art with respect to obtaining coatings of a single layer or multiple discrete layers so exemplified by such patents as U.S. Pat. Nos. 3,170,810, 3,335,030; 3,561,993; 3,573,960; 3,664,948; 3,775,285; 3,904,503; 3,933,644; 4,102,768; and 4,303,489 (all of which are incorporated herein by reference), copies of which are submitted herewith, where the coatings may be varied in shape and/or thickness. However, none of these patents are directed to obtaining a composite coating of the type obtained with the present invention where the relative percentages of the components change through the thickness of each layer of one or more layers.